The spinal column is a biomechanical structure composed primarily of support structures including vertebrae and intervertebral discs and soft tissue structures for motive and stabilizing forces including muscles and ligaments. The biomechanical functions of the spinal column include support, spinal cord protection, and motion control between the head, trunk, arms, pelvis, and legs. These biomechanical functions may require oppositely designed structures. For example, the support function may be best addressed with rigid load bearing structures while motion control may be best suited for structures that are easily movable relative to each other. The trade-offs between these biomechanical functions may be seen within the structures that make up the spinal column. Damage to one or more components of the spinal column, such as an intervertebral disc, may result from disease or trauma and cause instability of the spinal column and damage multiple biomechanical functions of the spinal column. To prevent further damage and overcome some of the symptoms resulting from a damaged spinal column, a spinal fixation device may be installed to stabilize the spinal column. Furthermore, the damage may extend between more than two vertebrae (levels). Damage across multiple levels requires spinal constructs that may span across those levels.
The damage that occurs in the spine may not be homogenous through a vertebra. Portions of the vertebra may be better suited to provide support for a spinal fixation construct. Traditionally, spinal constructs have used a single rod to extend the length of the construct. Thus, when a multi-level construct is implanted, the placement of the bone anchors is at least partially limited by the shape of the rod. Either a surgeon must bend a rod to fit within the bone anchoring members across the spinal levels, or the surgeon must try to place the screws along a relatively linear path along the length of the construct which may not be the best choice based on the underlying bone.
Spinal surgeries may also correct deformities in the spine. Such surgeries involve manipulating vertebra to move the curves of the spine inline. In prior art systems, spinal manipulations occur along the entire construct, necessitated by the spinal rod extending along the entirety of the spinal construct. Generally, the manipulation begins with capturing the rod near the ends and working toward the middle of the construct. The rod is captured along the length in adjacent levels as the vertebra in the central portions of the vertebral column is captured. Such systems require manipulation of the rod as well as manipulation of the vertebral segments along the length.
The description herein of problems and disadvantages of known apparatuses, methods, and devices is not intended to limit the invention to the exclusion of these known entities. Indeed, embodiments of the invention may include, as a part of the embodiment, portions or all of one or more of the known apparatus, methods, and devices without suffering from the disadvantages and problems noted herein.